1. Field of the Invention
The invention relates generally to telecommunications and videoconferencing. More specifically, the invention relates to telecommunications interfacing and provisioning for using compatible videoconferencing standards.
2. Description of Related Art
The Public Switched Telephone Network (PSTN) which facilitates voice (using telephones) and/or data (using modems) telephony throughout the world has in recent times been utilized to also deliver videoconferencing information. Towards that end, a standard has emerged for videoconferencing within the PSTN environment. This standard, known as the H.324 Recommendation, entitled "Terminal for Low Bitrate Multimedia Communication," specifies the usage of modems for videoconferencing over the PSTN, and thus, is referred variously in this specification as an "analog-modem based videoconferencing protocol." Prior to the H.324 recommendation, ISDN, or Integrated Services Digital Network, had been developed to evolve beyond ordinary PSTN modem networks. ISDN provides two "B" channels each of which can carry analog-encoded (ordinary voice telephony but not analog modem) information or digital (carrying data) signals. The advantage of ISDN over PSTN is that since ISDN is a digital transfer medium, the channels can be "bonded" or combined to provide a single channel with nearly twice the bandwidth of a single channel. Since each ISDN "B" channel provides up to 64 kilobits per second bandwidth, 2 bonded "B" channels can deliver 128 kilobits per second, which is much higher than the 33.6 or 56 kilobits per second currently given as the upper limit for V.34 modems operating over PSTN. To take advantage of the added bandwidth of ISDN, a new videoconferencing standard over ISDN known as the H.320 Recommendation, entitled "Narrowband Visual Telephone Systems and Terminal Equipment" was developed.
When a user at one node of a videoconferencing session communicates with another user at the other node over the same type of carrier, either ISDN or PSTN, the session can be carried out translationless since both nodes will utilize the same protocols. FIG. 1, however, shows that, when a node 110 utilizes an ISDN adapter 140, and consequently, the H.320 protocol, while the other node 120 uses an analog modem 130, and consequently, the H.324 protocol, a serious compatibility problem arises: the terminal at node 110 will be utilizing H.320 protocols while the terminal at node 120 will be expecting to receive H.324 protocols. Additionally, there is a modulation incompatibility since node 110 using ISDN (digital) modulation while node 120 uses analog modem type modulation. Though an ISDN channel can be used for analog voice telephony, the voice data is nonetheless digitized when being carried over the network. While the A/D (analog-to-digital) and subsequent (D/A) of voice telephony signals has been successfully achieved, the same cannot be said of analog modem signaling, such as V.34 (ITU-T (CCITT) Recommendation V.34, entitled "A Modem Operating at Data Signaling Rates of up to 28,800 bits/s for use on the General Switched Telephone Network and on Leased Point-To-Point 2-Wire Telephone-Type Circuits, published 1994) compatible signaling. As a result, an analog modem signal transmitted to a digital ISDN node or device would be incomprehensible and, thus, not communicate any useful information for facilitating videoconferencing or any other activity requiring data decoding precision.
One proposed solution for these incompatibilities, illustrated in the prior art of FIG. 1, has been to build a gateway or gateways at telephone company switching centers (Telco 150) which convert H.320 data (generated by ISDN-based videoconferencing software 115) to H.324 (PSTN-based videoconferencing software 125) and vice versa. However, such gateways are expensive to build and maintain and significantly interfere with the overall connection speed and connection quality for the session. These gateways add extra delay because of the need for layers of buffering to accomplish the translations and subsequent data streaming. The gateways themselves are complicated components and currently, have not been widely implemented. As such, if one Telco region does not provide such gateways, nodes within that region will be incapable of videoconferencing to other modulation incompatible nodes. The modulation incompatibility hinders also the use of software protocol translation/conversion schemes that will essentially be translating/converting incoherent data streams.
Thus, there is needed a simple, low-cost method and apparatus which will allow an ISDN based node and a PSTN (analog modem based) node to carry out a videoconferencing session without the need for protocol translation and gateways.